Since \(|h_i|\)  is a zero mean Nakagami-\(m\)  distributed RV, the variance of the received signal, given by (REF ), is a sum of squared Nakagami-\(m\)  RV with probability density function (PDF) given by [1]}
\(f_{\sigma ^2}(y) = \sum _{i=1}^{L}\sum _{k=1}^{a_{i}} \Xi \left(i,k\right) \frac{\left(y-c\right)^{k-1}}{b_i^k\left(k-1\right)!}\exp \left(-\frac{y-c}{b_i}\right),\) 
